I have one of those RAM stem mounts that I had on my ZX6, but couldn't get it to work on the C14. 12mm is just a little too small to get it into, so I modified the plastic nut on the end of it to fit in there. It seems to only be 12mm hex for a short distance and then widens out a large round hole. I got it in there, but it didn't seem very secure. I went with one of the RAM ball mounts that go on the handlebar base like this:
http://www.ram-mount.com/CatalogResults/PartDetails/tabid/63/partid/082065077045066045051054055085/Default.aspx